The present invention relates to medical devices in general, and in particular to atherectomy devices for removing occluding material from a patient""s blood vessels.
Arteriosclerosis is a common vascular disease in which a patient""s blood vessels become hardened and blocked by plaque or clots that impede blood flow. Left untreated, this condition is a major contributing factor to the occurrence of high blood pressure, strokes and cardiac arrest.
Many invasive and non-invasive techniques have been developed to treat arteriosclerosis. For example, cardiac bypass surgery is now a commonly performed procedure whereby an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is generally successful, it is fairly traumatic because the entire chest cavity must be opened to access the occluded vessel. Therefore, the procedure is not generally performed on elderly or relatively frail patients.
One example of a promising minimally invasive technique that can be performed on a greater number of patients is to remove the occluding material from a patient""s vessel in an atherectomy procedure. To perform this procedure, a guide catheter is typically inserted into the patient""s femoral artery and advanced until the distal end of the guide catheter is located in the patient""s ostium. A guide wire is then inserted through the guide catheter and traversed into the coronary arteries and past the occluded material to be treated. Then, as described in U.S. Pat. No. 4,990,134, issued to Auth, an atherectomy catheter having a small abrasive burr is advanced through the guide catheter and over the guide wire to the point of the occlusion. The burr is then rotated at high speed and passed through the occlusion to remove particles that are sufficiently small such that they will not re-embolize in the distal vasculature. As the burr removes the occlusion, a larger lumen is created in the vessel and blood flow is restored.
It is well recognized that the risk of certain patient complications increases with the size of the guide catheter through which minimally invasive devices are routed. Larger guide catheters require larger access holes in the femoral artery, creating the potential for patient complications, such as the sealing of the puncture site after completion of the procedure. Therefore, physicians generally wish to utilize the smallest possible guide catheter during a procedure. However, the smaller size guide catheters can only accommodate corresponding smaller size ablation burrs. Therefore, if a large vessel is to be treated, a larger burr and corresponding larger guide catheter must be used to successfully remove all of the occlusion from the patient""s vessel.
In addition, it has also been discovered that when performing an atherectomy procedure as described earlier, it has been beneficial to remove only a small amount of the occlusion at a time. Therefore, currently many procedures are performed using multiple passes through the occlusion with different sized ablation burrs. While these procedures have proven effective, the use of multiple devices for a single procedure adds both time and cost to the procedure.
One solution to the above mentioned problems associated with the existing atherectomy devices have been addressed by the development of an atherectomy device that can treat different size vessels while being traversed through a small guide catheter. This has been achieved by using a burr with a polymeric tube section that expands due to mechanical, hydraulic, or rotational means. An abrasive material is coated to the outside of the burr to provide a textured surface that can ablate the occlusion in a patient""s vessel.
However, the advances in development of atherectomy burr devices have created several difficulties in making and using the expandable burr device. The polymeric tube section of conventional expandable burr devices have been plated with an abrasive material using common plating techniques such as high-vacuum plasma deposition. However, these techniques are expensive, extremely complicated, and provide less adhesion between the abrasive and the polymeric substrate than generally desired. Further, it has been difficult to control the degree of expansion of the polymeric material, resulting in over-expansion of the burr at high rotational speeds. Over-expansion of the burr may stretch the burr beyond its elastic range resulting in a permanent, non-recovery deformation of the burr. Therefore, there is a need for an improved burr with the ability to expand to a predetermined maximum diameter during the operation of the burr while further providing an improved and more economical method of securing the abrasive material to the outside of the burr.
To eliminate the need for a physician to utilize larger guide catheters in order to route a larger diameter ablation burr in a patient, while solving the abovementioned deficiencies of the conventional expandable burr, the present invention comprises an improved expandable ablation burr including a flexible material with metal reinforcement fibers embedded therein. The expandable ablation burr is coated with an abrasive to ablate a new lumen in a patient""s vessel. The ablated diameter of the patient""s vessel preferably has a diameter that exceeds the diameter of a guide catheter through which the burr is routed.
According to one aspect of the present invention, the ablation burr comprises a flexible polymeric tube that expands as the burr is rotated. Metal reinforcement fibers are embedded within the tube to control the shape of the tube during expansion and to provide a predetermined maximum diameter of the expandable burr. The size of the burr changes in accord with the centrifugal force that is developed during rotation of the burr. Metal reinforcement fiber within the flexible polymeric tube improves the strength of the burr while preventing over-expansion of the burr.
In another aspect of the invention, the ablation burr comprises a flexible polymeric tube that is coated with an abrasive material. Metal reinforcement fibers within the polymeric tubing are exposed to allow the plating of the abrasive material to the tube. A portion of the exposed reinforcement is plated with an abrasive such that the tube will ablate an occlusion as the burr is rotated and advanced through a vessel. Plating metal is more economical than plating a polymer and provides a greater adhesion force between the abrasive coating and the burr. As the burr is rotated, the elastomeric tube expands by centrifugal force, thereby increasing the maximum outer diameter of the burr in order to create a larger lumen in a patient""s vessel.